NanoImprint Lithography (NIL) is not a novel technology anymore1 but huge progress has been achieved for its industrial introduction since its first reporting. One of the main evolutions concerns the use soft stamp media2 ,which is now a standard technology. EVG introduced this technology with a full wafer imprint solution (the size of the stamp corresponds to the size of the wafer to print)3 and results obtained since five years are at the state of the art. Repeatability, uniformity, sub-50nm resolution and high aspect ratio patterns are addressed at the same time4–6 . Nevertheless, some challenges still remain, as e.g overlay7 and in particular the distortion phenomenona 8 , which contribute to the remaining overlay next to global translation and rotation. This study is focused on distortion effect which appears during NIL process using flexible backplanes and its minimization by using different materials. A polymer backplane is compared with a glass backplane which are used as carrier to the soft stamp material. A dedicated methodology to precisely measure this distortion is implemented to remove global alignment signature. Distortion signature is firstly evaluated with a standard soft stamp material and process of reference already established. Distortion fingerprint mapping is obtained for each wafer. Thanks to this mapping, a monitoring distortion plot is extracted, in order to follow the evolution of the distortion depending on wafers (wafer-to-wafer) and lots (lot-tolot). This study highlights that the use of a glass backplane developed by EVG clearly allows to improve the distortion in terms of magnitude but also of stability.
We are developing a non-conventional retinal projector for augmented reality (AR) applications. In our concept, light at λ = 532 nm is guided in silicon-nitride (SiN) photonic integrated circuits (PICs) embedded in the lens of a pair of glasses. We use holographic elements to transmit the emissive points towards the user’s retina without using lenses. Pixels are formed in the eye using the self-focusing effect and the eye lens. The transparency of the device is an absolute requirement for our application. In this work, we present the fabrication and the characterization of our latest SiN PICs on transparent substrate. The device was fabricated by transferring the SiN PICs from a silicon to a glass substrate. We characterized the PICs and the free-space optical transmission properties of our device using in-house goniometers and a Modulation Transfer Function (MTF) setup. We found a 76% transparency at our wavelength and no image alteration. However, we measured significant waveguide propagation losses; solutions are discussed to tackle this problem. Our glass-substrate device is a major step towards a future prototype for our AR retinal projector.
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